DENVER -- A volunteer worker at the Denver Municipal Animal Shelter has been suspended as a result of accusations that he engaged in sexual activity with a dog, a city spokeswoman confirmed Wednesday.

The incident allegedly happened Saturday afternoon behind the building, and the man was partially naked when another shelter employee saw him, KMGH-TV in Denver reported.

The witness said Gustavo Castanon, 33, was having a basset hound perform a sex act on him, according to a police report.

Castanon was arrested on Wednesday and released on a $10,000 cash bond, said police spokesman Sonny Jackson.

Castanon faces one misdemeanor count of cruelty to animals.

"We can confirm that the volunteer was suspended and that we contacted both the Denver Police Department and the Denver District Attorney's Office to conduct an investigation," said Ellen Dumm, a spokesman for Denver Environmental Health, which oversees the shelter.

She would not comment further on the circumstances that led to the investigation request.

Police said they were informed of the allegations on Monday, and interviewed shelter employees as part of their investigation. The Denver District Attorney's Office is aware of the investigation, said spokeswoman Lynn Kimbrough.